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1. Field of the Invention
This invention relates to methods and devices intended to provide automatic protection from heat damage to tissues and materials which can result from the continuation of emissions from untended fiberoptics cables. Priorities often demand the casual placement of these cables, once they are detached from surgical implements and the like, and their distal ends may often rest on heat sensitive materials laid over portions of the human body to shield them from possibly damaging substances and/or to isolate them from sterile operating areas.
2. Background Information
The automatic control of hazardous emissions from the distal end of untended fiberoptics cables once they have been detached from implements such as used in surgical procedures, has been accomplished. Typically this has been by means which includes an autoclavable distal terminal that is divided to form two electrical contacts. These contacts are connected to a light control means by two narrow gauge wires included in the fiber bundle of the cable. Attachment of a conductive implement to the terminal completes the circuit to initiate emissions and detachment breaks the circuit to interrupt emissions.
In the applicant""s invention, the complexity and expense of an autoclavable, divided distal terminal is avoided. Conventional distal terminals may be used without modification other than their contact with the single narrow gauge wire, which is included in the fiber bundle of the cable and is preferably comparable in diameter to the fibers of the bundle. The wire connects the distal terminal with the proximal terminal which in turn is connected to the sensing terminal of a special proximity control circuit.
The applicant""s proximity control circuit is considered special, partly because it requires relatively few components to provide a stable, simply adjustable sensitivity to capacitive influence provided by substantial conductive masses through the earth-ground capacitance effect but there are functioning differences as well.
Like conventional proximity sensing circuits, the applicant""s circuit""s sensor permits triggering by both direct contact and near contact with substantial conductive masses. However, In the more conventional circuits tested, triggering is largely dependent on the areas of both surfaces involved. In the applicant""s circuit, while near contacts are affected by the extent of sensor area, direct contact is independent of surface areas and the circuit may be triggered by hand or other body part contact with no more than a narrow gauge sensing wire, which has a minimal area of sensing surface.
Also, while the conventional circuits tested and the applicant""s are triggered by direct sensor contact with a resistively coupled source of household a.c current, the applicant""s circuit is also triggered by a direct earth ground connection while the conventional circuits are not.
This proximity circuit is made to protectively interrupt the emissions from the distal end of a fiberoptics cable connected to a light source when the cable is disconnected from an implement using the light source, such as a surgical illuminating and viewing device. This is accomplished without breaking contacts of a control circuit as in other devices.
The applicant""s sensing circuit is adjusted so that direct body contact with the small metallic terminal at the distal end of the cable will initiate emission, but a casual contact with electrically shielded surfaces of the body will not. However, sensitivity is also such that a part of the body such as the hand, when electrically shielded by a surgical glove, can initiate emission by squeezing the terminal. This maximizes the proximity of the hand to the terminal by increasing the area of its proximity, removing any air spaces that might exist in the glove and perhaps even temporarily diminishing the thickness of glove material to a slight degree.
When a conductive implement is attached to the terminal the sensing surface is automatically increased so that pressures associated with normal manipulation of the implement is sufficient to maintain emissions. When the implement is removed and the cable set aside, the relatively small surface area is insufficient to cause the proximity sensing circuit to continue the emissions, even when resting on a large but shielded conductive mass, and the emissions are protectively interrupted.
The applicant""s special proximity sensing circuit requires only five components.
1. A relay to turn the light source on and off. Alternatively, an electrically actuated device to block and unblock light from the source. Prototype coil resistance about 3900 ohms.
2. A full-wave rectifier bridge which has its a.c. terminals connected to the a.c power source and in series with the a.c. coil of the relay or of the alternative electrically actuated light blocking device.
3. A sensitive gate silicon controlled rectifier (SCR) of a type requiring a maximum gate current (lgt) of 200 microamperes or less, having its anode and cathode connected to the d.c. terminals of the rectifier bridge.
4. A large value capacitor, preferably electrolytic, connected to the d.c. terminals of the rectifier bridge in parallel with the SCR.
5. A large value resistance to protectively limit potential current flow from the gate of the SCR to the accessible terminals of the fiberoptics cable and to adjust circuit sensitivity.
The applicant""s circuit takes advantage of SCR characteristics that exist under the conditions of low-load in the circuit as shown. Low-load is this context is a load typified by the load of the relay coil, the electromagnetic actuator of a light blocking element or the primary of a transformer supplying lower voltage to some other light blocking device requiring little energy. Even with the SCR of the prototype having a forward current rating of 10 amperes, and the bridge a rating of 1.5 amperes, a larger but still small resistive load such as a 15 watt incandescent bulb caused the circuit to lose sensitivity and a 60 watt incandescent bulb caused the circuit to turn on when energized and latch or maintain the on-state without the control option of an off-state. This would appear to preclude use of the circuit in a directly connected control of a light source requiring current of any substantial magnitude.
Increasing the value of the capacitor can cause a delay in the turn-off time which could be useful in instances where continuation of illumination needs to be maintained when hand proximity may have occasion to be briefly interrupted in the manipulation of an attached implement. The capacitor can be increased to approximately 10 mfd to achieve a turn-off delay of several seconds, but increases beyond this value may result in having the circuit latch, or delay its turn-off indefinitely.
The protection that the circuit provides can be made readily available for use with existing fiberoptics light devices by -adding the proximity control as a plug-in device to be connected between the receptacle of the power source and the plug of the fiberoptics lighting devices, and replacement of the conventional cable with a fiberoptics cable having wire connected terminals, and having its proximal terminal connected to the sensing terminal of the plug-in proximity control.
The protection that the circuit provides can also be made available as an addition to existing fiberoptics lighting devices without connecting the proximity control between the lighting device and its power source. When the sensor control employs a light blocking device in place of the power control of the relay, The proximity control circuit may be powered independently and attached to a special fiberoptics cable which includes a controllable light blocking device at its proximal terminal as well its wire connected proximal and distal terminals and is made to fit in place of the conventional cable.
An object of this invention is to provide a simple, positive protection of materials and patient tissues from heat damage resulting from the intense and concentrated emissions that issue from untended fiberoptics cables that are set aside following removal of attached implements such as those employed during surgery.
An associated object is to provide such protection from unwanted or hazardous emissions from fiberoptics cables in a way that requires the least modification of conventional equipment.
Another associated object is to provide this protection at the least possible expense.
Still another object is to provide protection that is automatic so that no operator attention is required.
Yet another object is to provide this protection without compromising the ability of the fiberoptics cable to be autoclaved in a sterilization process.
An additional object is to provide this protection by means of removable attachments, that modify existing equipment, so that such equipment may be used with or without the protection as a user option, according to purpose and need.